firmware: smccc: Add function to fetch SMCCC version

For backward compatibility reasons, PSCI maintains SMCCC version as
SMCCC didn't provide ARM_SMCCC_VERSION_FUNC_ID until v1.1.

PSCI initialises both the SMCCC version and conduit. Similar to the
conduit, let us provide accessors to fetch the SMCCC version also so
that other SMCCC v1.1+ features can use it.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Etienne Carriere <etienne.carriere@st.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Etienne Carriere <etienne.carriere@st.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20200518091222.27467-7-sudeep.holla@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

drivers/firmware/smccc/smccc.c

@@ -24,3 +24,8 @@ enum arm_smccc_conduit arm_smccc_1_1_get_conduit(void)
 
 	return smccc_conduit;
 }
+
+u32 arm_smccc_get_version(void)
+{
+	return smccc_version;
+}

include/linux/arm-smccc.h

@@ -100,6 +100,17 @@ enum arm_smccc_conduit {
  */
 enum arm_smccc_conduit arm_smccc_1_1_get_conduit(void);
 
+/**
+ * arm_smccc_get_version()
+ *
+ * Returns the version to be used for SMCCCv1.1 or later.
+ *
+ * When SMCCCv1.1 or above is not present, returns SMCCCv1.0, but this
+ * does not imply the presence of firmware or a valid conduit. Caller
+ * handling SMCCCv1.0 must determine the conduit by other means.
+ */
+u32 arm_smccc_get_version(void);
+
 /**
  * struct arm_smccc_res - Result from SMC/HVC call
  * @a0-a3 result values from registers 0 to 3